This invention relates to electro-optic transducers and optical transmission devices, and particularly to light-emitting and detecting transducers and light transmission systems therefor, and to devices and methods for aligning such systems and transducers. This invention also relates to fiber-optic cable, and particularly to termini, connectors, alignment devices and optical systems and methods for terminating and connecting fiber-optic cable.
The provision of optical transmission systems in the use of electro-optical transducers long has presented problems, particularly in communications systems using fiber-optic cable for transmission.
Coupling to electro-optical transducers has been complicated by the very small diameter of light beams transmitted as well as the small size of semiconductor devices often used to generate or detect the signals. Any foreign objects, such as dirt and dust, which accumulate in the optical path of the signals can seriously compromise the integrity and operability of the system.
Difficult problems specific to the use of fiber-optic cable for transmission also are well known. For example, providing suitable end termini and connectors for connecting two fiber-optic cables together long has been a demanding problem. The problem has been exacerbated by the prevalent use of single-mode fiber-optic light conductors of an extremely small diameter, such as 8 micrometers (0.008 millimeters). Aligning the cables accurately usually is a time-consuming and exacting process.
Standard commercial butt-joint type single-mode fiber-optic connectors suffer from numerous problems. First, they are relatively delicate, sensitive to dirt, difficult to clean, and easily damaged. The problems are even greater with multi-channel connectors which must function in a hostile environment.
In the past, various proposals have been made to improve such prior connectors. Included are proposals to use expanded-beam type connectors. Such connectors use different types of lenses to collimate and spread the beam of light emitted from the optical conductor. Then, an identical lens system is used to terminate another cable end to be coupled to the first cable, and the two termini are connected together. The second lens system re-focuses the beam on the second optical conductor so as to transmit the signal through the second cable.
The optical systems used in such prior expanded-beam connectors include spherical lenses, xe2x80x9cGRINxe2x80x9d lenses (graded index lenses) and molded aspheric lenses to expand and collimate the light beam.
The advantages of such expanded beam connectors includes minimizing the sensitivity to dirt and lateral misalignment and to the size of the gap between the ends of the optical conductors.
However, prior expanded beam connectors and techniques suffer from several problems. Such problems include relatively high optical losses and high cost. In fact, the cost has been considered to be prohibitive for many commercial applications. Furthermore, it is believed that the prior designs are relatively difficult or even impossible to be installed correctly in the field; that is, outside of a factory, laboratory, or other such facility.
Accordingly, it is an object of the present invention to provide an electro-optic transducer device, and a fiber-optic cable terminus, connector and alignment device and method which overcome or alleviate the foregoing problems.
More specifically, it is an object of the invention to provide an expanded-beam type terminus and connector and alignment device and method which overcome or reduce the problems experienced with prior expanded beam devices.
In particular, it is an object of the invention to provide an electro-optical transducer and fiber-optic cable terminus and connector which has as many of the following favorable attributes as possible: low cost; low loss; low back-reflection; small size; ruggedness; insensitivity to dirt; ease of cleaning; capability of being installed in the field; high optical power throughput capability; suitability for use in hostile environments; and capability of being standardized.
It is also an object of the invention to provide such a device and method capable of operating with single mode optical conductors; with multi-channel cable; is relatively non-dichroic; and preserves polarization of the light being conducted.
It is another object of the invention to provide an integrated multiple-reflector optical device for expanding and collimating light beams and particularly fiber-optic cable light beams.
In accordance with the present invention, the foregoing objects are met by the provision of an electro-optical transducer with an input/output optical transmission system in which the output is spread by a double-reflector optical system which avoids the problems of using refracting devices for such purposes.
The double-reflector system preferably is coupled to the transducer either directly, or through a light conductor such as a fiber-optic cable.
Preferably, the fiber-optic conductor and the double-reflector system are aligned with one another by coupling one of them to a magnetically permeable number and using magnetic flux to move the member.
The objects of the invention, as it relates to fiber-optic cable, also are met by the provision of a fiber-optic cable terminus, connector and alignment device and method as follows.
A terminus having a first reflector for reflecting the beam received from one optical conductor is provided. A second reflector reflects the beams from the first reflector to form expanded and collimated light beams.
Preferably, in both the transducer device and fiber-optic cable terminus, the system of reflectors is like that in a Cassegrainian or Ritchey-Chretien reflecting telescope system. Such systems have been used for many years in the field of astronomy. Applicants have recognized that, even though the telescope systems usually are very large and expensive, the small devices used in this invention can be made relatively inexpensively. The use of reflectors or mirrors rather than lenses tends to minimize the effects of refraction which so often increases the difficulty in the optical design process for the usual prior art proposals for beam-expanding connectors.
The resulting optical system is very compact, relatively amenable to standardization and inexpensive to manufacture.
In accordance with another feature of the present invention, the problem of aligning transducers or light conductors in fiber-optic cables is substantially alleviated by coupling a magnetically permeable element to the object to be aligned, applying a magnetic field to the magnetically permeable member, and controlling the field to move and align the objects with one another. Movement in at least two orthogonal axes is preferred.
Preferably, proper alignment is tested by passing a signal through the conductor and a second conductor, and determining when the signal transmission is maximized.
The optical conductor and the other components then are fixed in position relative to one another. Preferably, this is done by injecting a radiation-curable plastic material such as epoxy resin into the area surrounding the components, and irradiating the material to harden it when the alignment is correct. Specifically, an embodiment of the invention uses light-curable epoxy resin. Light is directed to the epoxy to perform the curing.
It also is preferred that the magnetic field source be one for developing a rotating magnetic field which rotates around the object to be aligned, with an electrical network being provided to control the field. This allows movement of the effective center of the magnetic field, and precise positioning of the object being aligned.
In one preferred embodiment, the magnetically permeable member is approximately toroidal or cylindrical, with a frustro-conical inlet to the central opening to guide the conducting fiber into the central opening during installation.
The invention also provides a compact integrated optical device for spreading and collimating light. A block of transparent material such as glass or plastic, is provided with surfaces shaped to form reflectors of the size, shape and position desired, and then those surfaces are coated with a reflecting material such as metal. This can be done at a reasonable cost by vapor deposition, sputtering, etc.
A problem often encountered in joining two ends of a fiber optic cable together is the problem of back-reflections of signals at the fiberglass-to-air interface between the ends of the cable cores.
This problem has been solved in the past by use of various techniques, such as rounding the ends of the fiber; making the ends very flat and butting the ends together to eliminate the air gap; filling the air gap with an index-matching gel, etc. Each of these methods has drawbacks.
It is believed that the interface between the air and the exit surface of the integrated reflector unit of this invention is subject to the same problem of back-reflections as any other light-transmitting solid-to-air interface. Therefore, it is another object of the invention to suppress such back-reflections without the disadvantages of the prior methods.
In accordance with another aspect of the invention, reflections are suppressed by giving the beam-spreading output surface of the light transmitting block a slight curvature so that the reflected beams are reflected along paths that are different from the paths taken by the rays to be collimated and focused. Therefore, they largely fail to reach the source point, and they are thus suppressed. As a result, a relatively high degree of suppression is achieved, without the use of a gel or other known techniques.
If desired, the broad input/output surface of the block also can be given an anti-reflective coating to aid in suppressing the reflections.
The foregoing and other objects and advantages of the invention will be set forth in or apparent from the following description and drawings.